Breakdown Criterion Research Articles

Investigation of temperature-dependent DC breakdown mechanism of EP/TiO2 nanocomposites

In dielectric science, the electrical breakdown strength of a polymeric material significantly decreases with elevated temperatures, which restricts the development of advanced electrical and electronic applications toward miniaturization. In the present study, to clarify the temperature-dependent DC breakdown mechanisms of epoxy resin (EP)/TiO2 nanocomposites, the effects of nanoparticle incorporation and temperature on charge transport and molecular chain dynamics were studied. The results indicate that space charge accumulation and electric field distortion are reduced by nanoparticle incorporation to enhance the deep trap level, while space charge accumulation, electric field distortion, and molecular displacement are all accelerated as temperature increases. To further investigate the influence of carrier traps and molecular chain dynamics on temperature-dependent breakdown, a DC breakdown simulation model that involves bipolar charge transport, molecular chain dynamics, and breakdown criterion equations is established. The calculated breakdown strengths of EP/TiO2 nanocomposites show great accordance with the experimental results, which indicates that temperature-dependent DC breakdown mechanisms are dominated by the synergetic effects of carrier traps and segment chain dynamics. Through the analysis of the breakdown model, a transition of the dominant mechanism (from segment chain to backbone dynamics) near the glass-transition temperature for DC breakdown of EP/TiO2 nanocomposites is discovered.

Optimization of coaxial gearbox parameters

The method of breaking down the gear ratio of a two-stage cylindrical coaxial gearbox is considered. The breakdown criteria are two overall indicators: the frontal area of the gearbox and its mass. The calculation results are approximated by power functions. Keywords: reducer, stage, gear ratio, Lagrange function, reducer optimization parameters. shevchenko6-32@yandex.ru, mukhovatiy@mail.ru, krolos@yandex.ru

Application of the Monte Carlo Method for the Determination of Physical Parameters of an Electrical Discharge

The aim of this paper is to use of the Monte Carlo Method to try to reproduce an electrical discharge in the oxygen gas; by following the random histories of free electrons and using the sampling laws, we can determine some electrical discharge parameters. Additionally we use the simulation results to verify the electrical breakdown criteria under an homogenous field and for small distances; and the obtained results are compared with those of the literature.

Modeling of Strong Wind-Sand Dielectric Streamer Discharge

Due to the complex and harsh climate environment in Northwest China, the external insulation of power lines and high-speed train are exposed to strong wind-sand environment all year round, which brings severe challenges to the external insulation design and protection of the electric systems. Based on the theories of streamer discharge, the plate-plate electrode was taken as the analysis object, and a theoretical physical model of the strong wind-sand dielectric discharge is established. In this model, the analytical expressions of electron ionization coefficient and positive ion generation coefficient in a wind-sand environment are deduced considering the combined effects of the airflow velocity, the distortion of the electric field caused by sand particles, and the electrons captured by sand particles in the discharge process; furthermore, the streamer breakdown criterion in wind-sand environment is proposed. Research results can provide an important theoretical basis for the quantitative calculation of the breakdown voltage and the external insulation protection in a strong wind-sand environment.

Analysis of Impact of Distributed Photovoltaic on Main Transformer Gap Protection

Distributed photovoltaic is one of the important energy supplies in new-type power system. Notably, when the main transformer is operated in non-directly grounded mode and distributed photovoltaic is connected to the low-voltage side, faults such as single-phase grounding short-circuit may cause overvoltage problems at the neutral point of the transformer, thereby posing a threat to the insulation at the neutral point. For the main transformer neutral point voltage offset and gap protection problems, this paper first analyzes the fault characteristics of the network, the operation of the line protection and the neutral point voltage offset after the fault occurs. Furthermore, combined with the distributed photovoltaic output characteristics after the near-system protection action, this paper analyzes that the distributed photovoltaic access after the line protection action may cause the neutral point over-voltage offset to deteriorate further. Moreover, under different matching degrees of distributed capacity and local load, the degree of neutral point voltage deviation when a single-phase fault occurs in a substation with distributed photovoltaic is derived. On this basis, the criterion of gap breakdown of the main transformer and relevant suggestions for installing gap protection are given. Finally, based on the simulation analysis of the single-phase ground fault of the grid-connected line, the boundary of neutral breakdown at different fault moments are obtained, thereby effectively guiding distributed photovoltaic to access new-type power system friendly.

Quantitative Analysis of Breakdown Criteria of Nd2Fe14B Compounds During Electromagnetic Vibration and Their Frequency-Dependent Solidification Structures/Magnetic Properties

Quantitative Analysis of Breakdown Criteria of Nd2Fe14B Compounds During Electromagnetic Vibration and Their Frequency-Dependent Solidification Structures/Magnetic Properties

Study of Shock Wave Development in Cold Flow of Gas Circuit Breaker for Improving Capacitive Current Switching

Abstract Capacitive current switching performance of SF6 circuit breaker is determined by combined action of gas flow and electric field in interruption chamber. Computational fluid dynamics method is used to study the development of shock waves inside a SF6 circuit breaker under the condition of capacitive current switching. It was found that a shock wave exists and travels with the pin contact during the contact opening. Existence of shock waves reduces the local gas density around contact head, while the contact head is also stressed by high electric field at the same time. If the region of low gas density coincides with the region with high electric strength, local dielectric performance will be significantly reduced. Using E/ρ as the dielectric performance index, when the local value of E/ρ exceeds the gas breakdown criterion, it will result in restrike to the capacitive current switching. The causes of high E/ρ are studied by analyzing the shock waves during the sequential periods of contact travel. Since the gap between the pin contact and nozzle throat strongly affects the strength of shock wave, the behavior of gap is studied with the calculation of E/ρ to find its influence on capacitive current switching.

Withdrawal from Negotiations as the Basis for Pre-Contractual Liability under Russian and Foreign Law

The paper analyzes the criteria for unfair termination of negotiations as a basis for pre-contractual liability. There are 3 components of unfair interruption of negotiations: 1) entry into negotiations without the intent to conclude an agreement and their subsequent interruption; 2) arbitrary termination of negotiations if the counterparty has confidence in the conclusion of the contract; 3) untimely notification of the counterparty about withdrawing from the negotiation process. The author analizes the criteria for unfair breakdown of negotiations. They include the following: the counterparty has reasonable confidence in the conclusion of the contract and the absence of a valid reason for terminating business contacts. These criteria are relevant only for the second composition of the elements of unfair termination of negotiations. To be held liable for entering into negotiations without intending to conclude an agreement and for the subsequent withdrawal from them, it is not required to establish such criteria, and in case of untimely notification of the severance of business contacts, it is necessary to establish only one criterion, namely, the counterparty can reasonably believe in conclusion of the agreement. As a general rule, participants in pre-contractual relations have the right to conduct parallel negotiations with other persons. This possibility may be limited by entering into an exclusivity agreement. At the same time, in some cases, entering into parallel negotiations can be qualified as unfair behavior even without the conclusion of such an agreement.

Polarity dependence of electrical breakdown in argon under a non-uniform electric field

A considerable difference in the breakdown potential of a uniform pressure gas (specifically argon) under an asymmetric non-uniform electric field is observed depending on the polarity of the field. The degree of variation in the breakdown potential between the two polarities can be explained if one assumes a strong variation of the ion-induced secondary electron emission coefficient with the magnitude of the reduced electric field at the cathode. The magnitude of the breakdown potential can be predicted by evaluating the breakdown criterion along multiple field lines if one includes a numerical factor to account for diffusion of electrons out of the preferred breakdown channel.

Plasma initiation and preliminary magnetic control in the HL-2M tokamak

The first plasmas have been achieved in the HL-2M tokamak by fulfilling the usual criteria for plasma breakdown, i.e. optimal working gas pressure, field null configuration of poloidal magnetic field, reasonable toroidal electrical field and clean wall conditions. The characterization of plasma initiation, such as identification of initiation time and position, is performed by diagnostic data analysis and numerical simulation. A model-based method, which enables dedicated pick-up sensors to estimate plasma radial position in real time, is applied for the limiter plasma shape in the first plasma commissioning phase. For a circular cross-section plasma, feedback control on plasma current and radial position allowed us to extend discharge durations to ∼250 ms associated with a 120 kA plasma current in flat-top. Preliminary plasma equilibrium reconstruction by the NICE code from pick-up sensors and flux loops, as well as interferometry measurements, gives plasma boundaries, plasma profiles of toroidal current density and safety factor, as well as electron density, in an offline way.

Comparison of parameters of the electric strength of air in a surface antenna during the radiation of single microwave pulses of various shapes

When substantiating the requirements for the radiation parameters of high-power microwave generators it becomes necessary to assess their maximum permissible values, conditioned to air breakdown in the radiating surface antenna. To predict the parameters of the dielectric strength of air, a theory based on a model of microwave pulses with a rectangular envelope is widely used. However, in practice, there are cases when the shape of the pulse envelope of the generator differs significantly from the rectangular. The aim of this work is to evaluate and compare the amplitude and energy parameters of the electric strength of air in the surface antenna of a high-power relativistic microwave generator when pulses are emitted with envelopes of various shapes. Pulses with rectangular, trapezoidal, parabolic and Gaussian envelopes were selected as the initial ones. The breakdown parameters were found based on the criterion of pulsed breakdown of gases and the regularity connecting the electron density with the pulse amplitude. The problem is solved numerically. In the range of pulse durations typical for high-power relativistic microwave generators, the dependences of the breakdown field and the maximum allowable energy on the pulse duration under normal atmospheric conditions are determined. The regularities connecting the maximum permissible energy and the breakdown field for the considered pulses are determined. With the same breakdown fields, a pulse with a Gaussian envelope has the highest maximum permissible energy, and a pulse with a rectangular envelope has the lowest.

Local well-posedness and break-down criterion of the incompressible Euler equations with free boundary

In this paper, we prove the local well-posedness of the free boundary problem for the incompressible Euler equations in low regularity Sobolev spaces, in which the velocity is a Lipschitz function and the free surface belongs to C 3 2 + ε C^{\frac {3}{2}+\varepsilon } . Moreover, we also present a Beale-Kato-Majda type break-down criterion of smooth solution in terms of the mean curvature of the free surface, the gradient of the velocity and Taylor sign condition.

Effect of Secondary Ionization Coefficient on the Breakdown Voltage in Nitrogen Gas

A theoretical investigation of the secondary ionization coefficients that responsible for the ionization current growth in uniform electric field studied. Nitrogen gas was from the range of E/p various 60 to 392 V/cm Torr, which corresponding to low values of pressures (0.05 < p < 0.684 Torr). The secondary ionization coefficients have been calculated using the breakdown criterion condition for a discharge gap in a uniform electric field. Using theoretical values of the primary ionization coefficient determined from numerically solving Boltzmann equation together with the values of the sparking distance (ds) obtained from present work. The program provided all cross-sections data from nitrogen. Experimentally, the measurement of breakdown voltage was taken after fixing sparking distance at ds= 69 cm. The results of the present work showed that, the value of breakdown voltage decreased during the increase of the secondary ionization coefficient value. Furthermore, under very low-pressure range, and within the studied sparking distance ds, the value of secondary ionization coefficient was negligible. During pressure increase, the value of secondary ionization coefficient becomes a saturation value.

Electric field dependence of SF6 nonlinear discharge characteristics: N-curve estimations

The N-curve of SF6 describes the relationship between the AC breakdown voltage in an extremely inhomogeneous electric field and pressurized SF6 gas. It is directly dependent on the electric field distribution, which is determined by the gas gap, curvature radius, and background electric field. An increase in gap distance, a decrease in curvature radius, and relatively weak background electric field are all conducive to corona stabilization. The electrode curvature radius is the determining factor in the positive glow corona (PGC) discharge quenching pressure. The breakdown voltage dominated by the streamer mechanism can be estimated accurately by calculating the electric field based on the Deutsch assumption and combining it with the SF6 static field breakdown criterion. The proposed method is applicable to the estimation of N-curves in gaps with varying field distributions. The work presented in this paper may support further quantitative research on the discharge mechanism of strongly electronegative gas dielectrics.

Parameters of the electric strength of air in a surface antenna during the emission of an ultrahigh-frequency pulse with a trapezoidal envelope

On the basis of the breakdown criterion and the equation of continuity of electrons in air, the amplitude and energy parameters of the electric strength of air in the surface antenna of a powerful microwave relativistic generator are determined when pulses are emitted with a trapezoidal envelope. Triangular and rectangular envelopes were considered as boundary cases of a trapezoidal envelope. The dependence of the parameters of electric strength on the shape of the envelope has been established. The calculation of the dependences of the breakdown field and the maximum permissible energy in a flat aperture on the pulse duration in the range of realizable durations of powerful relativistic microwave generators is carried out. For the same duration, the largest breakdown field has a pulse with a triangular envelope, and the smallest a pulse with a rectangular envelope. Wherein a pulse with a triangular envelope has the lowest maximum permissible energy, and a rectangular one has the highest. The relationships between the maximum permissible energy and the breakdown field for the pulses under consideration are determined. With the same maximum permissible peak amplitude, the highest energy has a pulse with a triangular envelope, and the smallest a pulse with a rectangular envelope.

Relative entropy based breakdown criteria for hybrid discrete velocity Bhatnagar–Gross–Krook and lattice Boltzmann method

In the present paper, novel breakdown criteria for the assessment of the validity of the continuum-fluid approximation are proposed. The approach is based on relative entropy (Kullback–Leibler divergence). The considered variants of the Kullback–Leibler divergence assess the contribution of non-hydrodynamic components of the gas velocity distribution function to the overall entropy. In addition, the chi-square statistic is introduced as a breakdown variable. As benchmark problems, the plane Couette and force driven Poiseuille flows are considered for various Knudsen and Mach numbers. The modeling is performed with the difference scheme for the kinetic Bhatnagar–Gross–Krook equation and the hybrid approach: the Bhatnagar–Gross–Krook equation is applied in non-equilibrium regions, and the lattice Boltzmann method is applied as the continuum-fluid method. The simulation results show that the proposed criteria can efficiently separate equilibrium and non-equilibrium domains.

DYNAMICS OF LAYER-BY-LAYER DESTRUCTION OF CARBON PLASTIC BY LIGHTNING CURRENTS: THEORY AND EXPERIMENT

On the basis of two models of lightning currents spreading on carbon plastic, the criteria of material destruction are determined. One of the models – the anisotropic conductive medium model from the Laplace equation with specified Neumann boundary conditions – makes it possible to obtain an exact solution in the form of Bessel functions for longitudinal and transverse current densities and to consider the material destruction zones by the radius and the depth. The model adequately describes the experiment with different arrangement of electrodes simulating the passage of lightning currents on constructions made of conductive composite and metal. The second – the model of composite layered structure – is constructed using the diagram of carbon plastic substitution and makes it possible to find the distribution of currents by a numerical method. The results of the calculations for both models are well consistent. The dynamics analysis of carbon plastic destruction revealed the criteria of destruction with parameters of real carbon plastic and experiment data that do not contradict the parameters of carbon plastic destruction obtained in foreign experimental studies. These criteria allow to determine the dependence between the value of the current integral and the number of layers of the composite material. Options with a small number of layers and with a large one when the reach-through breakdown criterion is possible were taken into account. Comparison of calculated and experimental destruction data showed good curve matching. The obtained criteria make it possible to predict the effects of lightning exposure under different material parameters and to take measures to improve the lightning resistance of carbon plastic products at the stage of aircraft design.

Breakdown at Multiple Protrusions in SF6 and CO2

The electric breakdown at single and multiple protrusions in SF6 and CO2 is investigated at 0.4 and 0.6 MPa, respectively. Additionally, the breakdown fields at rough surfaces of two different areas were determined. From the measurements, breakdown probability distributions for single protrusions were determined and fitted by Weibull distributions. This allowed the determination of statistical enlargement laws for the 50% breakdown probability fields E50. Such enlargement laws describe, for example, the scaling of breakdown field with electrode area or number of protrusions. The predictions were compared to the experimental data, and both agreement and discrepancies were observed depending on polarity and number of protrusions and gas. Discharge predictions including first electron, streamer inception and crossing, as well as leader propagation, gave further insight to this. It was found that predictions from enlargement laws based on statistical processes may not describe the measured breakdown fields well and that relevant physical breakdown criteria must also be considered.

A mechanism of electric charge losses in adiabatically compressed ferroelectrics

A ferroelectric depolarized by high strain-rates induced by the passage of adiabatic shock waves releases a high-density electric charge, initiating the generation of high voltage and megawatt power levels. Additionally, this depolarization process alters physical and mechanical properties that might cause energy and electric charge losses in the ferroelectric materials. We report, herein, the results of an experimental study of electric charge losses in Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 and Pb0.99(Zr0.52Ti0.48)0.99Nb0.01O3 ferroelectrics subjected to shock compression. We found that electric charge losses mainly occur in the compressed zone of ferroelectric elements; i.e., shock compression is an essential part of the charge loss mechanism. Based on our analysis of the experimental results, charge losses are explained by the leakage current flowing through microscopic conductive pathways (conductive channels), which are formed due to the effects of high magnitude stress and high electric fields in compressed zones of ferroelectric elements. It is shown that the Joule heating of conductive channels by the leakage current increases their temperature and conductance, eventually short-circuiting the electrodes of the shocked ferroelectric element and causing electric breakdown. The leakage current density, jleak, and breakdown delay time, tcr, can be described by the relationship, jleak2tcr=β (where β is the material dependent constant), over a wide range of delay times. The breakdown criterion we propose is based on the integral of specific current action and can be used to characterize the electric breakdown in a broad range of shock-compressed ferroelectric materials.

The Causes and Mechanisms of the Ukrainian Crisis of 2014: A Structural–Demographic Approach

Author(s): Shevsky, Dmitry | Abstract: This article tests the hypothesis that Ukraine experienced a state breakdown in 2014. The methodology employed to test this statement is based on achievements of structural-demographic theory, created by Jack Goldstone and developed by Peter Turchin. The reasons for a fiscal crisis, intra-elite conflict and mass mobilization (the three criteria for a state breakdown) are discussed. It is demonstrated that budget management in Ukraine was ineffective, and, coupled with an unbalanced political system, led to the fiscal crisis. The intra-elite conflict was caused by Yanukovych’s politics and by lack of resources as a consequence of elite overproduction, which led to fewer opportunities among the traditional elites. To demonstrate the mass discontent that was the main factor for the protests and rallies, evidence is presented that the population of Ukraine experienced immiseration in 2010–13. The final factor determining the future of the Ukrainian system was the delegitimization of power. This could happen only under the conditions of intra-elite conflict. All of these factors arose because of the high degree of capital concentration in the hands of the economic elite. The article concludes that we have every reason to say that a state breakdown occurred in Ukraine.